The mechanisms by which long chain fatty acids (FA) permeate the plasma membrane of adipocytes have been recently partially characterized in our laboratory. Permeation occurs predominantly by a protein mediated, saturable mechanism and, to a small extent, by simple diffusion. It is now proposed to determine whether permeation is physiologically a rate-controlling step for FA metabolism and release, and whether the process is altered by catecholamines, ACTH and glucocorticoids. The existence of a transport mechanism for FA in cells types other than adipcoytes will be investigated. FA permeation in hepatocytes, muscle and 3T3 cells will be studied. Identification of a membrane protein as a FA transporter will be attempted. FA transport is blocked by DIDS (an inhibitor of anion transport in rbc) and the irreversible binding of [3H]-DIDS to the adipocyte membranes will be further exploited to characterize and isolate the transporter. Its identity with the anion inorganic and monocarboxylate anion transport protein(s) of erythrocytes will be investigated. In general, permeation will be assayed by the initial rate of intracellular accumulation of unesterified fatty acids in cell suspensions incubated in media containing various concentrations of unbound FA. Techniques for limiting metabolism of FA, suppressing membrane fluxes of FA and separating rapidly cells from incubation medium have been developed. Transport will also be assayed by measuring the influx or efflux of alpha-bromopalmitate, a non-metabolizable FA, which is competitive with natural FA for transport.